The lens driving device in the present mini-camera is similar with the subject disclosed in the Chinese patent No. ZL200410017724.3 titled “Lens Driving Device”. It comprises an annular magnet carriage disposed on a base, in which a magnet and a coil are disposed and a lens with lens holder which is mounted in the coil, the section of the annular magnet carriage is hollowed-U-shaped, and the magnet and the coil are disposed in magnet carriage, wherein the coil is fixed around the lens holder, while the lens holder is movably received in the annular magnet carriage. The lens driving device of above mentioned patent also comprises an annular flat front spring, an annular flat rear spring, a small cap and a frame, the outer edges of the front spring and the rear spring joint with the annular magnet carriage, the small cap makes the inner edge of the front spring being fixed on the lens holder, the frame makes the outer edge of the front spring being fixed on the annular magnet carriage.
When the coil is powered on, the electromagnetism force generated by the coil when powered on can resist with the pre-pressed the front spring and the rear spring, and makes the lens holder moving along the optical axis.
The lens driving device of above mentioned patent still comprises a vertical restricting device which is mounted in the space between the small cap and the frame to prevent the lens holder being offsetting and moving, and a rotating restricting device which is mounted in the space between the lens holder and the annular magnet carriage to prevent the lens holder being offsetting and moving.
The above mentioned lens driving device utilizes the function of magnetic induction, then, the lens holder mounted in the annular magnet carriage can move under the parallel electromagnetism force, meanwhile, the opposite resilient force is generated by the front spring and the rear spring mounted on the lens holder, when said electromagnetism force and said elastic force are in balance, the lens holder will be held in a predefined position, then, the camera can focus automatically.
For the above mentioned lens driving device, the manufacture, assembling, displacement are all required to reach high precision. Although the lens holder can be restricted so as to having the ability of resisting jounce and impact and having high image quality with no additional component, the above mentioned lens driving device still has following shortcomings:
Firstly, the space occupied by the frame restricts the shape of the annular magnet carriage, it will reduce the efficiency of the electromagnetism induction and restrict the micromation of camera;
Secondly, being a base body, the base and the lens holder should be manufactured in high precision size, furthermore, the shape of the base and the lens holder are complex, so it is very difficult to reach high precision in manufacture and assembling;
Thirdly, the front spring and the rear spring are in offsetting along the same annular orient, so that, when the springs move forward and backward, they will make distortion and generate a force of rotation at the same orient that will cause the rotation and excursion of the lens holder.
Lastly, to assemble the above mentioned lens driving device requires many procedure, and the precision and the capability of the product can be tested only after the assembling is finished, so that the qualification rate of products will not be easy to control efficiently. That will certainly cause the waste of the resource.